The present invention relates, in general, to electronics, and more particularly, to electron emission devices.
One of the recent advances in vacuum microelectronics led to the use of nanotubes as electron emitters. Typically, nanotubes are fine filaments made from carbon as disclosed by Cees Deckker, Carbon Nanotubes as Molecular Quantum Wires, Physics Today, pp. 22-28, May 1999. The nanotubes can be applied to a substrate to function as electron emitters.
Typically, the nanotubes disposed on the substrate have differing lengths and also a random orientation, thus, the distance from the electron accumulation anode to each nanotube varies. The current versus voltage characteristics for each nanotube is determined by the nanotube length and the distance from the end or tip of the nanotube to the anode. Because each of the nanotubes have different lengths, different voltages are required to produce electron emission from each nanotube. One nanotube emitter may require a higher voltage to produce electron emission than an adjacent nanotube emitter that has a longer length. Voltage required to produce electron emission generally varies greater than one hundred percent from one nanotube emitter to another. This voltage variation makes it difficult to control the turn-on voltage of a vacuum microelectronic device utilizing the nanotube emitters.
Accordingly, it is desirable to have a method of forming nanotube emitters that provides a low voltage variation (generally less than ten percent) between the nanotube emitters.